As a structural material for enhancing building strength, for example, concrete reinforced with rebars or the like has been used for the outer walls etc. of multi-dwelling units such as apartments, single-family homes, various school facilities, and commercial buildings.
Since concrete has heat-retention and cold-retention properties, there are disadvantages in that building interiors are warmed by heat retained in summer or are cooled as a result of cooling concrete in cold winter seasons. In order to reduce such long-term influence of outdoor temperature on building interiors through concrete, concrete is usually heat-insulated.
Accordingly, as a heat-insulating layer, a rigid polyurethane foam having flame retardancy against fire has been used.
Patent Literature (PTL) 1 discloses a flame-retardant urethane resin composition comprising a polyisocyanate compound, a polyol compound, a trimerization catalyst, a foaming agent, a foam stabilizer, and additives, wherein the trimerization catalyst is at least one member selected from the group consisting of nitrogen-containing aromatic compounds, carboxylic acid alkali metal salts, tertiary ammonium salts, and quaternary ammonium salts; and the additives are a combination of red phosphorus, which is essentially used as an additive, with at least one additive selected from the group consisting of phosphoric acid esters, phosphate-containing flame retardants, bromine-containing flame retardants, boron-containing flame retardants, antimony-containing flame retardants, and metal hydroxides.